The present invention relates to an apparatus for contacting semiconductor devices and circuits to be tested and more specifically, it relates to an improved probe having an integral fine probe tip, pressure spring, conductive line, and connector for contacting said semiconductor devices and a method of constructing the improved probe.
In the course of fabricating semiconductor devices and circuits it becomes necessary to electrically probe the devices and circuits to ascertain proper functioning and for analysis of parameters and determination of failure mechanisms. To accomplish this a finely pointed probe or group of finely pointed probes is brought into contact with the device, circuit wiring, or pads connected to the device or circuit.
A typical probe in wide use is formed by sharpening the end of a fine tungsten wire to a pointed tip. This wire is then mounted in a spring loaded manipulator. As semiconductor devices become smaller and circuits denser it becomes difficult make electrical contact with the device, circuit wiring, or pads for two reasons. Firstly, the probe tips may be too dull or blunt to make contact only to the intended the device, circuit wiring, or pads connected to the device or circuit and the device, circuit wiring, or pads. Secondly, the probe tips or wires from which they are fabricated are so thin as to bend when contact is attempted and slide off the intended contact point when sufficient pressure is placed on the probe tip to make low resistance electrical contact to the device, circuit wiring, or pads.
The present invention solves the foregoing problems by providing a finely pointed probe tip small enough to contact only the device, circuit wiring, or pads that combines both stiffness and means to prevent bending when pressure is applied.
The probe tip of the present invention has a body comprising a finely formed tip tapering to a point, a spring comprising horizontal and vertical members in the form of a serpentine and a connector for hookup to a tester. Normal semiconductor processes are used to fabricate the probe assembly, therefore the probes may be fabricated with tip dimension of a few microns and points in the sub-micron regime.
The monolithic body is formed from a materials such as polysilicon that may flex many times without breaking. Since this material may not be highly conductive, provision is made for a conductive line, typically a metal, running from the tip along the spring to the connector. Metal silicide may be applied to the tip to improve adhesion of the wiring to the monolithic body. The monolithic body is formed by either filling a trench in an oxide layer with a material such as polysilicon and after forming the metal lines and silicide, the body released by dissolving the oxide. Therefore it is an object of the present invention to provide monolithic micro probes having an integral fine probe points, pressure springs, conductive lines, and connectors for contacting semiconductor devices to be tested and a method of fabrication of such probes.
Probe tips fabricated by the method of the present invention may also be fabricated having single or double shielding layers effectively providing for coaxial and triaxial wiring up to the probe point. Several probe bodies may be formed at the same time, attached to each other in a tree. Instead of a conductive line, a first conductive layer may be deposited over the entire tree followed by alternating layers of insulator and further conductive layers, affording the capability of coaxial and triaxial protection to the signal in the main body or main body/conductive line. The tip would be selectively dip etched to remove the overlaying layers to expose the first conductive layer. Similar etching operations would be performed at the connector end. Therefore it is further object of the present invention to provide a micro probe having conductive shielding surrounding a central conductor surrounding an integral probe point, pressure spring, and connector.
After a coaxial version of the probe is fabricated, a Kelvin type probe may be fabricated by plating a conductor over the tip, electrically connecting the inner and outer conductors together at the very tip of the probe, while still maintaining its sharpness. Therefore it is still further object of the present invention to provide a micro Kelvin type probe having conductive shielding surrounding a central conductor that surrounds an integral probe point, pressure spring, and connector, wherein the inner conductor and outer shielding are electrically connected together at the probe tip.